The present invention relates to trouble diagnosis for an evaporated fuel treatment apparatus for an internal combustion engine which emits an evaporated fuel generated in a fuel tank to an intake system of the internal combustion engine, and specifically, to an evaporated fuel treatment apparatus for an internal combustion engine which detects leakage from the fuel tank and turns on a warning lamp, the apparatus turning off the warning lamp if the leakage is caused by a large leakage and if no leakage is subsequently detected.
Japanese Patent Application Kokai No. Hei 10-37815 presents methods for judging the presence of leakage from a fuel tank. One of the methods comprises detecting the pressure of the fuel tank a number of times and judging the presence of leakage if the detected values concentrate in neighborhoods of the atmospheric pressure while judging the absence of leakage if the detected values deviate significantly from the atmospheric pressure in a positive or negative direction. Thus, whether there is leakage or not can be easily judged without reducing the pressure of the fuel tank.
Another method for judging whether there is leakage from a fuel tank comprises reducing the pressure of the fuel tank down to a predetermined value, then closing the fuel tank. The absence of leakage is judged if the variation of the pressure of the fuel tank measured after closing the fuel tank is smaller than a predetermined value, while the presence of leakage is judged if the variation is larger than the predetermined value (this judgment process is called a leak checking process). In this case, in order to exclude the effects of vapors, the variation of the pressure caused by vapors must be considered as a correction value. This method enables the detection of leakage even from a very small hole with a diameter of 0.5 mm in a tank.
On the other hand, a large hole (i.e. a large leak) in the fuel tank is chiefly generated by a user""s failure to close a filler cap of a fuel tank and should preferably be handled separately from the above-mentioned detection for very small hole before issuing a warning to the user. Japanese Patent Application Kokai No. Hei 9-291856 describes a method for judging abnormality or malfunctioning of the fuel tank, wherein whether there is a large hole is judged. This method comprises reducing the pressure of the fuel tank down to a predetermined value, and calculating the variation of the pressure to check for leakage. The presence of a large hole is judged if the difference between the pressure of the fuel tank measured at the end of the pressure reducing process and the pressure measured within a predetermined period of time after the start of the leak checking process is larger than a predetermined value.
The above-mentioned method may judge the presence of a large hole even when the leakage is actually small or no leakage is actually occurring, for a combined reason associated with the amount of fuel fed and the variation of the flow rate of a purge control valve. In addition, even if the presence of a large hole is judged by a user""s error such as the user""s failure to close the filler cap, a MIL (warning lamp) is lit. When the user notices his or her failure and closes the filler cap, the MIL should be turned off while the above mentioned prior art lacks means for doing so.
It is therefore an object of the present invention to provide an evaporated fuel treatment apparatus that can accurately detect a large hole.
It is another object of the present invention to provide an evaporated fuel treatment apparatus that can turn off a warning light in a timely manner, if the detection of a large hole terminates while the warning lamp is lit since the large hole was detected.
Accordingly, according to an aspect of the present invention, an evaporated fuel treatment apparatus for an internal combustion engine is provided. The apparatus comprises an evaporated fuel discharge prevention system including a fuel tank, a canister having an opening to the atmosphere, a passage allowing the fuel tank to communicate with the canister, and a purging passage allowing the canister to communicate with the intake manifold of the engine. The apparatus also comprises a pressure sensor for detecting the pressure of the evaporated fuel discharge prevention system.
The apparatus further comprises a controller coupled to the pressure sensor for judging the presence of a first leak in the evaporated fuel discharge prevention system if a change in the pressure from the pressure sensor is small. The controller further checks a change in the pressure from said pressure sensor when said system is closed after placing the system under a negative pressure. The controller judges the presence of a large leak if the first leak is judged and the pressure increases instantaneously upon closing said system.
According to another aspect of the invention, the apparatus further comprises a warning lamp lit by the controller when the first leak is judged. The controller turns off the warning lamp when the presence of the large leak was detected in a previous judgment cycle, but any leak, including the first leak and the large leak, is not detected in the current judgment cycle.
According to further aspect of the invention, the presence of the first leak is judged if the pressure concentrates in neighborhoods of the atmospheric pressure.
According to another aspect of the invention, the presence of the large leak is judged if the difference between the pressure as detected when the system is placed under a negative pressure and the pressure as detected immediately after the evaporated fuel discharge prevention system is closed is greater than a predetermined value.
Furthermore, requirements for judging the presence of the large leak may include one or more of the following condition:
i) the difference, between the pressure as detected when the evaporated fuel discharge prevention system is opened to the atmosphere and the pressure as detected when the bypass valve is closed after said opening to the atmosphere, is smaller than a predetermined value,
ii) the difference, between the pressure as detected when the evaporated fuel discharge prevention system is opened to the atmosphere and the pressure as detected when the system is closed after placing the system under a negative pressure, is smaller than a predetermined value,
iii) the difference, between the pressure as detected immediately after the evaporated fuel discharge prevention system is closed and the pressure as detected a predetermined period of time after the system is closed, is smaller than a predetermined value,
iv) a period required for placing the evaporated fuel discharge system under a predetermined negative pressure is longer than a predetermined period.